(1) Field of the Invention
The present invention relates to a variable venturi type carburetor.
(2) Description of the Prior Art
In the conventional variable venturi type carburetor, for instance in a horizontal needle venturi type carburetor, as illustrated in FIG. 1, the throttle 3 is provided in one part of the horizontal fuel suction-ejection hole assembly 2, one end of which opens in the venturi unit 1; a tapered needle 5 running through the throttle 3 is provided in the suction piston 4 which is located opposite to the fuel suction-ejection hole 2 and can come into or out of the venturi unit 1; and the effective cross-sectional area of a gap formed between said needle 5 and said throttle 3 is utilized to gauge the fuel volume to be sucked or ejected. The suction piston 4, which moves in accordance with the sucked volume of air in the suction system, serves to keep the negative venturi pressure nearly constant.
In the conventional carburetor of this type, however, the top end of the fuel path 7, the bottom end of which opens in the float chamber 6, opens into the fuel suction hole 2 upstream of the throttle 3. Therefore, when idling continues under high temperature, steam bubbles 8 generated in the fuel collect in the fuel suction-ejection hole 2 and they coalesce and collect to block the throttle 3, with the result that the mixture becomes steadily lean. Further, the mixture becomes suddenly lean with passage of steam bubbles through the throttle 3, which is liable to cause hunting of the air/fuel ratio as indicated in the characteristic curve A of FIG. 2. As a consequence the engine is liable to lose stability in idling, and in the worst cases, it may come to a stall.